The invention relates to a conduit for the transport of cryogenic media, and to a method of manufacturing a such conduit.
A conduit for the transport of cryogenic media is known from European Patent Application 0 326 923 which comprises two corrugated metal pipes arranged concentrically and spaced apart from one another, and spirally wound superinsulation made of alternating superposed layers of metal foil or metallized plastic film and insulation material, for example fiberglass non-woven fabric, being situated in the annular gap between the metal pipes and the annular gap being evacuated. The vacuum is created for example by pumps in the annular gap, the pump connection being made at the end of the conduit or on both ends of the conduit.
Because of the tightly packed superinsulation intended to hold the pipes in a concentric arrangement, the pumping procedure is very lengthy.
Accordingly, in European Patent Application 0 326 923 separate spacing is provided between the inner pipe and the first layer of the superinsulation winding, which significantly accelerates the evacuation process. This procedure enables conduits up to 100 m in length to be economically evacuated.
The development of new superconducting materials which enter the superconducting state at temperatures above 50° K. has made superconducting cables economical by greatly lowering the cost of cooling.
The conduit according to European Patent Application 0 326 923 is superbly suited as a “cryogenic envelope” for superconducting cables due to the fact that it combines good flexibility, a good insulating effect, and a simple cable manufacturing technique. Such superconducting cables are economical only if it is possible to manufacture lengths greater than 100 m, preferably up to 500 m, depending on the diameter. However, lengths greater than 100 m cannot be economically evacuated according to the current state of the art.